truct ListNode* trainningPlan(struct ListNode* l1, struct ListNode* l2) {
    if (l1 == NULL)
        return l2;
    if (l2 == NULL)
        return l1;
    struct ListNode* head = NULL;
    struct ListNode* tail = NULL;
    while (l1 && l2)
    {
        if (l1->val < l2->val)
        {
            if (head == NULL)
            {
                head = l1;
                tail = l1;
            }
            else
            {
                tail->next = l1;
                tail = l1;
            }
            l1 = l1->next;
        }
        else
        {
            if (head == NULL)
            {
                head = l2;
                tail = l2;
            }
            else
            {
                tail->next = l2;
                tail = l2;
            }
            l2 = l2->next;
        }
    }
    while (l1)
    {
        tail->next = l1;
        tail = l1;
        l1 = l1->next;
    }
    while (l2)
    {
        tail->next = l2;
        tail = l2;
        l2 = l2->next;
    }
    return head;
}